Orthogonal Frequency Division Multiplexing (OFDM) technology is a multicarrier modulation communication technology in essence and is one of the core technologies for the 4th generation mobile communication. A multipath channel of an OFDM has a characteristic of frequency selective fading in a frequency domain. In order to overcome the frequency selective fading, a channel is divided into a plurality of OFDM subchannels in the frequency domain, wherein the frequency spectral characteristic of each subchannel is approximately flat, and all the subchannels are orthogonal to each other, therefore frequency spectrums of the subchannels are allowed to be overlapped with each other, thereby not only the problem of selective fading is overcome, but also the utilization degree of the frequency spectrum resource is improved.
A Long Term Evolution (LTE) system is an important program of the 3rd Generation Partnership Project (3GPP). When the LTE system adopts a normal cyclic prefix, a time slot includes 7 uplink/downlink symbols and has a length of 7 uplink/downlink symbols, and when the LTE system adopts an extended cyclic prefix, a time slot includes 6 uplink/downlink symbols and has a length of 6 uplink/downlink symbols.
A Resource Element (RE) is a subcarrier on an OFDM symbol, 12 contiguous subcarriers and 7 contiguous OFDM symbols constitute a downlink Resource Block (RB) which is 180 kHz in the frequency domain and has a time length of a normal time slot in a time domain, as shown in FIG. 1. When the LTE system performs resource allocation, a resource block is taken as a basic unit for allocation. Wherein when an extended cyclic prefix is adopted, the number of contiguous OFDM symbols comprising an RB is 6.
The LTE system supports the MIMO application of four antennae, and the corresponding antenna port #0, antenna port #1, antenna port #2 and antenna port #3 respectively adopt a method of full bandwidth Cell-Specific Reference Signals (CRSs). When the cyclic prefix is a normal cyclic prefix, the positions of these cell-specific reference signals in a physical resource block are shown in FIG. 2(a). When the cyclic prefix is an extended cyclic prefix, the positions of these cell-specific reference signals in a physical resource block are shown in FIG. 2(b). In FIG. 2(a) and FIG. 2(b), the horizontal coordinate 1 represents a sequence number of a subframe on an OFDM symbol.
In addition, a UE-specific reference signal is also provided, which is transmitted only in the time-frequency domain position where a UE-specific Physical Downlink Shared Channel (PDSCH) is located. Wherein the functions of the cell-specific reference signal include quality measurement for downlink channel and downlink channel estimation, i.e., the quality measurement and demodulation for a downlink channel.
A base station needs to measure the position of User Equipment (UE) in a cell, so that it can perform effective configuration and scheduling for the UE. At present, the CRS is adopted for measuring the terminal, thus some limitations exist as follows:
(1) CRS sequence repeats in each frame, so the mutual correlation is poor;
(2) when the transmission is performed with two antennae, the maximum multiplexing factor is 3, and the interference between the adjacent cells is large;
(3) the CRS power is semi-static configured, so the positioning performance is limited.
At present, a solution used to solve the above problems is to position the UE by transmitting a Position Reference Signal (PRS), and thus ensure the positioning precision of the UE. However, in the existing technologies, only the physical resource which uses a resource block as a unit to transmit a position reference signal is defined, and the positions in all the resource blocks where the position reference signal is transmitted are the same, whereas as for how to transmit the position reference signal, such as transmitting the resource block index of the position reference signal, the specific time-frequency position in the resource block, and the sequence of the reference signal and the like. No specific solution has been provided yet.
For this reason, it is urgent to provide a specific method for transmitting a position reference signal in the industry to ensure the positioning precision of the UE.